The following invention relates to a mobile perimeter monitoring system and in particular relates to a two-station transmission system whereby the range between a fixed or mobile transmitter and a fixed or mobile receiver may be continuously monitored.
The adult supervision of young children can become a complicated task when the adult supervisor is busy with other chores and/or has a number of persons in his or her care. Children are, by their nature, curious, and frequently wander off to explore or become lost. For example, it is sometimes difficult for parents to monitor the whereabouts of their children in a large and crowded area such as a shopping mall. Children may be given instructions to stay in a certain area, but sometimes the instructions are not followed.
Some of these same concerns are shared by pet owners who would like to know, at least within certain limits, the whereabouts of pets. Dogs and cats, like children, become curious or distracted and frequently wander beyond their normal perimeters. In addition, there are safety applications where it would be useful to know the locations of individuals such as skiers, hikers or hunters.
In the past, transmitter/receiver combinations have been available whereby a transmitter carried by a child or pet continuously transmits a signal to the receiver. The transmitter is designed to have a fixed transmission range, and when it moves outside of that transmission range, an alarm at the receiver sounds. The devices that have been heretofore available are only partially useful for this purpose and have numerous drawbacks. First, these devices have had but a fixed transmission range which is set by the manufacturer. For example, if the manufacturer decides that the range will be one-quarter mile, that range will have to suffice under all circumstances. However, in certain circumstances the parent might wish that the range be set lower so that the effective perimeter could be limited to a much shorter range. Also, if multiple transmitters are used, it may become impossible to know whether one of the transmitters has moved outside of the perimeter since other transmitters within the perimeter may prevent the alarm from going off. Since the transmission frequencies available for this type of device are limited and comprise a very narrow FM band, the possibility for adjacent transmitters to interfere with one another is very high. Finally, tracking a lost child can be difficult and can consume the battery power of the receiver because the alarm is activated whenever the child is out of range.